1. Field of the Invention
This invention relates to the removal of contaminants from organic liquids. In one of its more particular aspects it relates to the removal of halogenated aromatic hydrocarbons from oils. In another of its more particular aspects, this invention relates to the removal of polyhalogenated biphenyls such as polychlorinated biphenyls (PCB's) from oils used as dielectrics in electrical equipment and the destruction of the polyhalogenated biphenyls removed.
2. Prior Art
Polyhalogenated biphenyls, referred to hereinafter as PCB's, have been used in electrical equipment such as transformers and capacitors as non-flammable dielectrics. Since the discovery that PCB's were carcinogenic, teratogenic, and mutagenic, however, many transformers and capacitors formerly filled with PCB's have been drained and innocuous materials, such as highly refined mineral oils or silicone oils, substituted in their place. However, traces of polychlorinated biphenyls and other contaminants, such as polybrominated biphenyls (PBB's) remain in the oils as a result of incomplete cleaning of the equipment prior to substitution of the oils. Since the hazardous character of PCB's and similar materials has been determined to affect liquids contaminated with very small amounts of such materials, it has become necessary to purify such contaminated oils. Current Federal regulations require that any material contaminated with 500 ppm or more of PCB's must be handled, stored and disposed of by the same procedures as PCB's themselves. Materials contaminated with 50-500 ppm of PCB's are classified as PCB-contaminated materials and can be disposed of by burning in utility boilers of greater than 500,000,000-Btu/hr rated capacity. Materials containing less than 50 ppm of PCB's are classified as non-PCB materials and do not require extraordinary disposal procedures. Thus it is desirable to reduce the concentrations of PCB's in transformer oils and similar materials to below 500 ppm and preferably to below 50 ppm.
Processes for separating various types of halogen-containing compounds from liquids are known.
U.S. Pat. No. 2,203,690 discloses a process for removing water-immiscible liquids such as ethylene chloride from water-miscible liquids such as alcohols and ketones by diluting the mixture to be treated with water and passing the diluted mixture through activated carbon.
U.S. Pat. No. 3,862,900 discloses a process for adsorbing chlorine from hydrocarbons containing about 0.001 to 0.2 wt. % of chemically combined chlorine by passing the hydrocarbons through a bed of molecular sieves having an effective pore size in the range of 7 to 11 Angstrom units.
PCB's and PBB's in particular have been treated by various methods.
U.S. Pat. No. 3,881,295 discloses a process for disposing of PCB's and other chlorinated materials by means of a liquid swellable solid synthetic resinous polymer.
U.S. Pat. No. 4,230,053 discloses a process for destroying PBB's by means of a thermit reaction which utilizes an iron-containing waste byproduct from steel production, a mineral acid and a reducing metal such as aluminum, magnesium or manganese to provide temperatures of at least about 3000.degree. F. (1650.degree. C.).
U.S. Pat. No. 4,353,793 discloses the use of a mixture of a mono-capped polyalkylene glycol alkyl ether and an alkali metal hydroxide for reducing the level of PCB's dissolved in an organic solvent such as a transformer oil.
U.S. Pat. No. 4,353,798 discloses a process for removing PCB contaminants from silicone dielectric fluid by cooling a silicone dielectric fluid containing PCB contaminants to a temperature at which the resulting mixture separates into two phases, a silicone-rich phase and a PCB-rich phase. The PCB-rich phase is isolated by means of gravitational separation.
U.S. Pat. No. 4,387,018 discloses a process for removing PCB's from oil by extracting the PCB's into methanol.
U.S. Pat. No. 4,400,936 discloses a process for disposing of PCB's by subjecting them to combustion in a self-contained system utilizing a diesel engine or similar combustor which burns a mixture of fuel and PCB's. The system also utilizes liquid scrubbers for removing contaminants from the gases produced in the combustion. While the process of this invention effectively disposes of PCB's, it results in the combustion of a fuel along with the PCB's and requires the use of gas/liquid scrubbing apparatus.
PCB's have also been disposed of by decomposition in molten salts.
U.S. Pat. No. 4,246,255 discloses a process for the decomposition of PCB's using oxygen and a molten salt comprising an alkali metal carbonate and preferably also an alkali metal sulfate.
U.S. Pat. No. 4,447,262 discloses a process for the destruction of PCB's utilizing a molten salt comprising a mixture of a basic alkaline earth metal salt selected from the group consisting of alkaline earth metal oxides and carbonates together with an alkaline earth metal halide.
Processes are also known for removing contaminants from electrical equipment such as transformers.
U.S. Pat. No. 3,894,171 discloses the removal of sorbed water and gases from a transformer by means of a vacuum treatment which is carried out while the transformer is in operation.
Although various methods are known for removing halogenated hydrocarbons and especially PCB's and related materials from liquids contaminated therewith, none of the methods is wholly satisfactory for removing PCB's from transformer oils and similar materials which must be reclaimed for further use, none is completely acceptable for removing PCB's while the equipment containing them is in service and none is effective for destroying the PCB's in an economical manner after removal.